There are three conditions that are common for all available sleep modes. Ignition status = 0, Movement status = 0 and no link opened with a server.
Ignition status depends on your configured Ignition source. According to the title of your question I assume that you are using power voltage as Ignition source. In most vehicles the battery voltage is around 12.5 V when ignition is turned off and over 13.5 V when it is turned on. Knowing the voltages of your battery should allow you to set thresholds (High/Low voltage) accordingly in order to correctly monitor vehicle ignition status.
Movement status depends on your configuration as well. Once your selected source is not detecting movement, Movement Stop Delay (configurable in System tab) starts to count down. After the timeout passes, device movement status changes to 0 and another sleep condition is met.
In order for the device to close link with the server, Open Link Timeout (Configurable under GPRS settings) has to pass. Send period In On Stop data acquisition mode has to be at least 90 seconds longer than Open Link Timeout in order to close link successfully.
There are a few more conditions that have to be met (https://wiki.teltonika.lt/view/FM3001_Sleep_modes). Once all sleep mode conditions are met, the device starts counting down the configured Sleep Mode Timeout. After it passes the device enters sleep mode.
While in any sleep mode except Ultra Deep Sleep, the device will still generate and send records to the server according to On Stop Min/Send period. If a high priority eventual record is generated, it will be sent to the server immediately as well. After sending records in sleep mode, all of the timeouts are skipped and the device goes back to sleep right after. While in Ultra Deep Sleep, no records will be sent.